Medical tubes and methods of manufacture

ABSTRACT

This invention relates to a medical tube comprises an elongate conduit having a first opening, a second opening, a longitudinal axis, a lumen extending between the first opening and the second opening along the longitudinal axis, and a corrugated wall, formed from an extruded material, extending between the first opening and the second opening and surrounding the lumen. The wall is stiffer in a first length of the conduit adjacent the first opening than in a second length of the conduit adjacent the second opening. The variable stiffness of the tube wall can improve the thermal profile of the tube as well as improve drain-back of condensation into a humidifier providing humidified gas to the tube.

FIELD OF INVENTION

This disclosure relates generally to tubes suitable for medical use, andin particular to tubes for use in medical circuits suitable forproviding gases to and/or removing gases from a patient, such as inpositive airway pressure (PAP), respirator, anesthesia, ventilator, andinsufflation systems.

BACKGROUND TO THE INVENTION

In medical circuits, various components transport warm, humidified gasesto patients. For example, in some breathing circuits such as PAP orassisted breathing circuits, gases inhaled by a patient are deliveredfrom a heater-humidifier through an inspiratory tube. As anotherexample, tubes can deliver humidified gas (commonly CO₂) into theabdominal cavity in insufflation circuits. This can help prevent “dryingout” of the patient's internal organs, and can decrease the amount oftime needed for recovery from surgery.

In these medical applications, the gases are preferably delivered in acondition having humidity near saturation level and at close to bodytemperature (usually at a temperature between 33° C. and 37° C.).Condensation or “rain-out” can form on the inside surfaces of thebreathing tubes as the high humidity breathing gases cool and/or comeinto contact with the relatively cooler breathing tube surface. A needremains for tubing that insulates against heat loss and, for example,allows for improved temperature and/or humidity control in medicalcircuits.

It is therefore an object of the present invention to provide a medicaltube and/or method of manufacturing a medical tube which will go atleast some way towards addressing the foregoing problems or which willat least provide the industry or public or both with a useful choice.

In this specification where reference has been made to patentspecifications, other external documents, or other sources ofinformation, this is generally for the purpose of providing a contextfor discussing the features of the invention. Unless specifically statedotherwise, reference to such external documents is not to be construedas an admission that such documents, or such sources of information, inany jurisdiction, are prior art, or form part of the common generalknowledge in the art.

Further aspects and advantages of the present invention will becomeapparent from the ensuing description which is given by way of exampleonly.

SUMMARY OF THE INVENTION

Medical tubes and breathing tubes and methods of manufacturing suchtubes are disclosed herein in various embodiments.

In least one embodiment, a medical tube for providing humidified gas toa patient can comprise an elongate conduit having a first openingconfigured in size and shape to connect to a source of humidified gas, asecond opening configured in size and shape to connect to a patientinterface, a longitudinal axis, a lumen extending between the firstopening and the second opening along the longitudinal axis, and a wall,formed from an extruded material, extending between the first openingand the second opening and surrounding the lumen. The wall is stiffer ina first region of the conduit adjacent the first opening than in asecond region of the conduit adjacent the second opening.

In at least one embodiment, a heated breathing tube can comprise asingle, corrugated extruded conduit comprising a proximal, patient endand a distal, chamber end; and one or more heating elements on or in theconduit, wherein the conduit has a first region at the chamber end witha first stiffness and a second region at the patient end with a secondstiffness and the first stiffness is greater than the second stiffness.

In various embodiments, in the foregoing medical tube and/or heatedbreathing tube, the first region is configured to extend vertically froma source of humidified gas. The vertical extension can define adrain-back length. The drain-back length can be between about 350 mm andabout 400 mm, for instance.

In various embodiments, the foregoing medical tube and/or heatedbreathing tube have one, some, or all of the following properties, aswell as properties described elsewhere in this disclosure. The medicalor breathing tube can further comprise one or more conductive filamentsin or on the conduit. At least one of the one or more conductivefilaments can be a heating wire. At least one of the one or moreconductive filaments can be a sensing wire. The conduit can be generallycylindrical. The wall can be corrugated. The extruded material can befoam. The foam can be polymer foam. The foam can be closed-cell foam.The extruded material can comprise one or more surface modificationagents. The wall can have an average contact angle less than 50 degrees(or about 50 degrees). The thickness of the wall in the first region canbe between 0.5 mm and 2.0 mm (or about 0.5 mm and about 2.0 mm). Thethickness of the wall in the second region can be between 0.1 mm and 1.0mm (or about 0.1 mm and about 1.0 mm). The mass of the wall in the firstregion can be between 50 g/m and 110 g/m (or about 50 g/m and about 110g/m). The weight of the wall in the second region can be between 20 g/mand 50 g/m (or about 20 g/m and about 50 g/m). The volume of the wall inthe first region can be between 1.0 cm3/m and 2.0 cm3/m (or about 1.0cm3/m and about 2.0 cm3/m). The volume of the wall in the second regionis between about 0.2 cm3/m and about 1.0 cm3/m. The ratio of flexmodulus of the wall in the first region to flex modulus of the wall inthe second region can be between 10:1 and 250:1 (or about 10:1 and about250:1). Stiffness of the wall in a third region of the conduit betweenthe first region and the second region can be intermediate the stiffnessof the wall in the first region and the second region. The average wallthickness can be about 100 microns.

In various embodiments, the foregoing medical tube or heated breathingtube (including any or all of the above properties) have one, some, orall of the following properties, as well as properties describedelsewhere in this disclosure. The medical or breathing tube can furthercomprise a sheath surrounding at least a portion of an outer surface theelongate conduit. The sheath can comprise an extruded material extrudedaround at least a portion of the outer surface of the elongate conduit.The sheath can comprise a material generally spirally wrapped around atleast a portion of the outer surface of the elongate conduit. The sheathcan comprise a sleeve material sleeved around at least a portion of theouter surface of the elongate conduit. The sheath can comprise a sheathwall. The sheath wall can have a generally constant stiffness. Thesheath wall can be stiffer in a first region of the sheath than in asecond region of the sheath. The sheath wall can be stiffer proximatethe first opening of the conduit than the second opening of the conduit.The sheath wall can be stiffer proximate the second opening of theconduit than the first opening of the conduit. The sheath wall can bestiffer proximate the first opening and second opening of the conduitthan in an intermediate region of the conduit.

The foregoing medical tube according to an or all of the precedingembodiments can be incorporated into a breathing circuit or aninsufflation system, among other applications. The breathing tube can beincorporated into a breathing circuit, among other applications.

In at least one embodiment, a method of delivering humidified gas to apatient can comprise providing a single, corrugated extruded conduitcomprising a proximal, patient end, a distal, chamber end, heatingelements on or in the conduit wall, a first region adjacent the chamberend with a first stiffness, and a second region adjacent the patient endwith a second stiffness, the first stiffness being greater than thesecond stiffness; connecting the chamber end of the conduit to achamber, wherein the conduit in the first region extends vertically fromthe chamber; connecting the patient end of the conduit to a patientinterface; and delivering humidified air through the conduit. In variousembodiments, the conduit can have one, some, or all of the propertiesdescribed above with respect to the medical and breathing tubes, as wellas properties described elsewhere in this disclosure.

In at least one embodiment, a method of manufacturing a tube or conduitaccording to one, some, or all of the above embodiments comprisesextruding a tape, wherein a first length of the tape is thicker,heavier, or stiffer than a second length of the tape; spirally windingthe extruded tape around a mandrel such that adjacent turns of theextruded tape touch or overlap, thereby forming an elongate conduithaving a longitudinal axis and a lumen extending along the longitudinalaxis; corrugating and cooling the elongate conduit to form the medicaltube, the tube having a wall surrounding the lumen, wherein the wall isstiffer in a first region of the conduit adjacent a first end than in asecond region of the conduit adjacent the second end. As explainedabove, the wall can have a thickness between 0.5 mm and 2.0 mm (or about0.5 mm and about 2.0 mm in the first region). The wall can have athickness between 0.1 mm and 1.0 mm (or about 0.1 mm and about 1.0 mm)in the second region. The ratio of flex modulus of the wall in the firstregion to flex modulus of the wall in the second region can be betweenabout 10:1 and about 250:1.

In various embodiments, the foregoing method can have one, some, or allof the above tube or conduit properties, following properties, as wellas properties described elsewhere in this disclosure. The extruded tapecan comprise foam. The foam can be polymer foam. The polymer foam can beclosed cell. The extruded tape can comprise one or more surfacemodification agents. A surface of the wall facing the lumen can have asurface contact angle less than 50 degrees (or about 50 degrees). Themethod can further comprise spirally winding a reinforcement beadbetween adjacent turns of the extruded tape. The reinforcement bead cancomprise one or more conductive filaments. The method can furthercomprises spirally winding one or more conductive filaments around theelongate conduit.

In at least one embodiment, a method of manufacturing a tube or conduitaccording to one, some, or all of the foregoing embodiments comprisesextruding an elongate conduit having a longitudinal axis and a lumenextending along the longitudinal axis; and corrugating and cooling theelongate conduit to form the medical tube, the tube having a wallsurrounding the lumen, wherein the wall is stiffer in a first region ofthe conduit adjacent a first end than in a second region of the conduitadjacent the second end. In various embodiments, the foregoing methodcan have one, some, or all of the above tube or conduit properties, thefollowing properties, as well as properties described elsewhere in thisdisclosure. As explained above, the first region can be configured toextend vertically from a source of humidified gas. The verticalextension can define a drain-back length. The drain-back length can bebetween 350 mm and 400 mm (or about 350 mm to about 400 mm). In certainembodiments, the method can further comprise co-extruding one or moreconductive filaments, such that the one or more conductive filaments aredisposed on or in the conduit.

The term “comprising” as used in this specification means “consisting atleast in part of”. When interpreting each statement in thisspecification that includes the term “comprising”, features other thanthat or those prefaced by the term may also be present. Related termssuch as “comprise” and “comprises” are to be interpreted in the samemanner.

This invention may also be said broadly to consist in the parts,elements and features referred to or indicated in the specification ofthe application, individually or collectively, and any or allcombinations of any two or more said parts, elements or features, andwhere specific integers are mentioned herein which have knownequivalents in the art to which this invention relates, such knownequivalents are deemed to be incorporated herein as if individually setforth.

The invention consists in the foregoing and also envisages constructionsof which the following gives examples only.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments that implement the various features of the disclosedsystems and methods will now be described with reference to thedrawings. The drawings and the associated descriptions are provided toillustrate embodiments and not to limit the scope of the disclosure.

FIG. 1 shows a schematic illustration of a medical circuit incorporatingone or more medical tubes.

FIGS. 2A-2C show longitudinal cross sections of example composite tubes.

FIG. 3 shows a medical circuit demonstrating drain-back length of atube.

FIGS. 4A-4E illustrates test equipment for measuring the flex modulus oftubes.

FIG. 5A is a chart plotting test results for a tube sample having 100g/m mass.

FIG. 5B is a chart plotting test results for a tube sample having 40 g/mmass.

FIG. 5C is an enlarged plot of the linear portion of the flexure textplots of FIG. 5A.

FIG. 5D is an enlarged plot of the linear portion of the flexure textplots of FIG. 5B.

FIGS. 6-7 illustrate example placements of a heater wire.

FIG. 8 is a plot comparing the condensate accumulation inuniform-stiffness tubes to that in a variable-stiffness tube.

FIG. 9 shows an example medical circuit according to at least oneembodiment.

FIG. 10 shows an insufflation system according to at least oneembodiment.

FIG. 11 is a schematic illustration of a manufacturing method formedical tubing, including hopper feed, screw feeder to a die head, andterminating with a corrugator.

FIG. 12 is a schematic illustration of a spiral-forming manufacturingmethod for medical tubing.

Throughout the drawings, reference numbers are re-used to indicatecorrespondence between referenced (or similar) elements. In addition,the first digit of each reference number indicates the figure in whichthe element first appears.

DETAILED DESCRIPTION

Details regarding several illustrative embodiments for implementing theapparatuses and methods described herein are described below withreference to the figures. The invention is not limited to thesedescribed embodiments.

Breathing Circuit Comprising One or More Medical Tubes

For a more detailed understanding of the disclosure, reference is firstmade to FIG. 1, which shows a breathing circuit according to at leastone embodiment, which includes one or more medical tubes. Tube is abroad term and is to be given its ordinary and customary meaning to aperson of ordinary skill in the art (that is, it is not to be limited toa special or customized meaning) and includes, without limitation,non-cylindrical passageways. The breathing circuit incorporates one ormore variable-stiffness tubes, which may generally be defined as a tubehaving distinct stiffness at each end of the tube. Such a breathingcircuit can be a continuous, variable, or bi-level positive airwaypressure (PAP) system or other form of respiratory therapy.

Gases can be transported in the circuit of FIG. 1 as follows. Dry gasespass from a ventilator/blower 105 to a humidifier 107, which humidifiesthe dry gases. The humidifier 107 connects to the inlet 109 (the end forreceiving humidified gases) of the inspiratory tube 103 via a port 111,thereby supplying humidified gases to the inspiratory tube 103. Aninspiratory tube is a tube that is configured to deliver breathing gasesto a patient, and may be made from a variable-stiffness tube asdescribed in further detail below. The gases flow through theinspiratory tube 103 to the outlet 113 (the end for expelling humidifiedgases), and then to the patient 101 through a patient interface 115connected to the outlet 113.

An expiratory tube 117 also connects to the patient interface 115. Anexpiratory tube is a tube that is configured to move exhaled humidifiedgases away from a patient. Here, the expiratory tube 117 returns exhaledhumidified gases from the patient interface 115 to the ventilator/blower105.

In this example, dry gases enter the ventilator/blower 105 through avent 119. A fan 121 can improve gas flow into the ventilator/blower bydrawing air or other gases through vent 119. The fan 121 can be, forinstance, a variable speed fan, where an electronic controller 123controls the fan speed. In particular, the function of the electroniccontroller 123 can be controlled by an electronic master controller 125in response to inputs from the master controller 125 and a user-setpredetermined required value (preset value) of pressure or fan speed viaa dial 127.

The humidifier 107 comprises a humidification chamber 129 containing avolume of water 130 or other suitable humidifying liquid. Preferably,the humidification chamber 129 is removable from the humidifier 107after use. Removability allows the humidification chamber 129 to be morereadily sterilized or disposed. However, the humidification chamber 129portion of the humidifier 107 can be a unitary construction. The body ofthe humidification chamber 129 can be formed from a non-conductive glassor plastics material. But the humidification chamber 129 can alsoinclude conductive components. For instance, the humidification chamber129 can include a highly heat-conductive base (for example, an aluminumbase) contacting or associated with a heater plate 131 on the humidifier107. By way of example, the humidifier 107 may be a standalonehumidifier, such as any of the humidifiers in the respiratoryhumidification range of Fisher & Paykel Healthcare Limited of Auckland,New Zealand.

The humidifier 107 can also include electronic controls. In thisexample, the humidifier 107 includes an electronic, analog or digitalmaster controller 125. Preferably, the master controller 125 is amicroprocessor-based controller executing computer software commandsstored in associated memory. In response to the user-set humidity ortemperature value input via a user interface 133, for example, and otherinputs, the master controller 125 determines when (or to what level) toenergize heater plate 131 to heat the water 130 within humidificationchamber 129.

Any suitable patient interface 115 can be incorporated. Patientinterface is a broad term and is to be given its ordinary and customarymeaning to a person of ordinary skill in the art (that is, it is not tobe limited to a special or customized meaning) and includes, withoutlimitation, masks (such as tracheal mask, face masks and nasal masks),cannulas, and nasal pillows. A temperature probe 135 can connect to theinspiratory tube 103 near the patient interface 115, or to the patientinterface 115. The temperature probe 135 monitors the temperature nearor at the patient interface 115. A heating filament (not shown)associated with the temperature probe can be used to adjust thetemperature of the patient interface 115 and/or inspiratory tube 103 toraise the temperature of the inspiratory tube 103 and/or patientinterface 115 above the saturation temperature, thereby reducing theopportunity for unwanted condensation.

In FIG. 1, exhaled humidified gases are returned from the patientinterface 115 to the ventilator/blower 105 via the expiratory tube 117.The expiratory tube 117 can also be a variable-stiffness tube, asdescribed in greater detail below. However, the expiratory tube 117 canalso be a medical tube as previously known in the art. In either case,the expiratory tube 117 can have a temperature probe and/or heatingfilament, as described above with respect to the inspiratory tube 103,integrated with it to reduce the opportunity for condensation.Furthermore, the expiratory tube 117 need not return exhaled gases tothe ventilator/blower 105. Alternatively, exhaled humidified gases canbe passed directly to ambient surroundings or to other ancillaryequipment, such as an air scrubber/filter (not shown). In certainembodiments, the expiratory tube is omitted altogether.

Variable-Stiffness Tubes

FIG. 2A shows a longitudinal cross section of example variable-thicknesstube 201. In general, the medical tube 201 comprises an elongate conduit203 having a first opening 205, a second opening 207, and a longitudinalaxis LA-LA. In this example, the elongate conduit 203 has a generallycylindrical shape. Nevertheless, “conduit” is a broad term and is to begiven its ordinary and customary meaning to a person of ordinary skillin the art (that is, it is not to be limited to a special or customizedmeaning) and includes, without limitation, non-cylindrical passageways.A lumen 209 extends between the first opening 205 and the second opening207 along the longitudinal axis LA-LA. The conduit 203 is stifferadjacent the first opening 205 than it is adjacent the second opening207.

The conduit 203 comprises a wall 211, extending between the firstopening 205 and the second opening 207, and surrounding the lumen 209.In this example, the wall 211 is stiffer in a first region 213 of theconduit 203 adjacent the first opening 205 than in a second region 215of the conduit 203 adjacent the second opening 207. The wall 211 can beoptionally corrugated, or of a corrugate profile. As shown in thisexample, the corrugation profile can comprise of alternating outercrests (or annular protrusions) and inner troughs (or annular recesses).The outer crests can correspond to a location of maximum inner radiusand maximum outer radius of the elongate conduit, and the inner troughscan correspond to a location of minimum inner radius and minimum outerradius of the elongate conduit. Such corrugations may be of an annularcorrugation or spiral corrugation form. Alternatively, the wall 211 canbe of a smooth or non-corrugated profile. Optionally, the first opening205 is configured in size and shape to connect to a source of humidifiedgas, such as a humidifier described above, and the second opening 207 isconfigured in size and shape to connect to a patient interface. Forinstance, one or more ends can be configured to connect to a connectionport which facilitates connection to the patient interface and/orhumidifier. Other configurations can also be desirable. For example, inother embodiments, the first opening 205 can be configured to connect toa patient interface, while the second opening 207 can be configured toconnect to a ventilator/blower, as described above.

As described in greater detail below, the tube 201 can optionallyinclude one or more conductive (heating or sensing) filaments. Optionalpositions for the filaments are: placed within the lumen, typically in aloose, spiral fashion; placed in close external contact to the tubewall, typically in conjunction with an external sheath to secure theconductive filaments) in place and prevent heat loss; or embedded in thetube wall.

The increased stiffness of the tube at one end can lead to bettermanagement of condensate by improving “drain back.” Furthermore, theincreased stiffness is linked to properties that improve the insulatingprofile of the wall, such as increased thickness, mass, and/or volume.Thus, for unheated tubes or tubes with heating filaments placed withinthe lumen, the first end is preferably the humidifier end to betterinsulate the tube against heat loss where most of the condensationoccurs. This configuration also adds stiffness to the tube where itexits the humidifier, so it can maintain a more vertical position for agreater distance, before bending toward the horizontal. In this way,more condensation drains back to the humidifier, rather than enteringthe breathing tube. A thinner tube at the patient end improvesflexibility, reduces weight, and improves the comfort of the patient.

For heating filaments placed externally (e.g., on the tube wall radiallyopposite the lumen) or embedded in the wall, the second end ispreferably the humidifier end to allow heat from the elements to moreeasily penetrate the tube and heat the gas stream. An insulatingexternal sheath (described below) will typically be fitted to this typeof tube to prevent heat loss. A stiffer tube at the patient end isoffset by a thinner sheath to increase flexibility and reduce weight toimprove the user's comfort.

Thus, in use, the tubes according to the various embodiments lead toless condensate and also a greater range of ambient conditions wherethey can be used before condensation build up becomes a substantialissue.

In general, the total length of the tube can be between 1.0 m and 3.0 m(or about 1.0 m and 3.0 m) or between 1.0 and 2.0 m (or about 1.0 and2.0 m). Preferably, the length of the tube is 1.5 m (or about 1.5 m) or1.8 m (or about 1.8 m). Preferably, the average diameter of the lumen(accounting for the variability in diameter created by the crests andtroughs in optional corrugation) is between 10 mm and 30 mm (or about 10mm and 30 mm). Preferably, the lumen diameter is 20 mm (or about 20 mm)or 22 mm (or about 22 mm). In fact, it is contemplated that thevariable-stiffness tubes described herein can be used as a replacementfor tubes previously used in the art, which typically have an averagelumen diameter between 10 mm and 30 mm and length ranging between about1 m and 2.5 m.

It is also preferable that the tube be resistant to crushing, resistantto restrictions in flow when bent, resistant to kinking, resistant tochanges in length and/or volume under internal pressure, resistant toleaking (<25 mL/min at 6 kPa), have low flow resistance (the increase inpressure at maximum rated flow is less than 0.2 kPa), and beelectrically safe. Preferably, the tube can be bent around a 25 mmdiameter metal cylinder without kinking, occluding, or collapsing, asdefined in the test for increase in flow resistance with bendingaccording to ISO 5367:2000(E).

Stiffness

Referring again to FIG. 2A, preferably, a first region 213 of theconduit 203 adjacent the first opening 205 is stiffer than a secondregion 215 of the conduit 203 adjacent the second opening 207. Variousembodiments include one or more additional regions between the firstregion 213 and the second region 215 having different stiffnesscharacteristics than the first region 213 and the second region 215 (forexample, stiffness characteristics intermediate those of the firstregion 213 and the second region 215). A three-region tube 201, forexample, can impart a better curving profile in comparison to atwo-region tube 201. A three-region tube 201 schematic is shown in FIG.2B. This example comprises a third region 221 intermediate the firstregion 213 and the second region 215.

The first region 213 and/or the second region 215 can be an absolutedistance, such as 5 cm or 10 cm (or about 5 cm or 10 cm). The firstregion 213 and/or the second region 215 can also represent a relativedistance. In at least one embodiment, the first region 213 comprises10-30% (or about 10-30%), or 30-50% (or about 30-50%), of the totallength of the tube 201 (where for example, the total length of the tube201 is the distance from the first opening 205 to the second opening207, exclusive of cuffs or connectors 223 or any other separate terminalcomponent attached to the end of the tube 201). For example, the firstregion 213 can comprise 33% (or about 33%), or 35% (or about 35%) of thetotal length of the tube 201 (where for example, the total length of thetube 201 is the distance from the first opening 205 to the secondopening 207). In at least one embodiment, the second region 215comprises 5-15% (or about 5-15%), or 15-50% (or about 15-50%), of thetotal length of the tube 201 (where for example, the total length of thetube 201 is the distance from the first opening 205 to the secondopening 205). For example, the second region 215 thereof comprises 10%(or about 10%), or 15% (or about 15%) of the total length of the tube201 (where for example, the total length of the tube 201 is the distancefrom the first opening 205 to the second opening 207). In at least oneembodiment of a standard 1.8 m tube 201, the first region 213 is 0.3-0.7m (or about 0.3-0.7 m) in length and preferably 0.5 m or thereabout, thesecond region 215 is 0.1-0.2 m (or about 0.1-0.2 m) in length andpreferably 1.15 m or thereabout, and a third region 221 intermediate thefirst region 213 and second region 215 is between 1.0-1.5 m in lengthand preferably 0.15 m or thereabout. In any event, the first region 213and second region 215 represent substantial lengths of the tube 201.

The difference in stiffness in these regions represents a significantdeparture from the prior art. A typical prior art delivery tube mightincorporate an extruded corrugated conduit. At an extremely localisedlevel, for example within the pitch of the corrugations, which istypically less than 1 cm, the stiffness of the conduit will vary. Thecorrugating process may result in a stiffer wall at the troughs of thecorrugations than the peaks. However, between the two ends of the tubeconnectors, the stiffness properties across any substantial length areessentially the same as the properties of any other substantial lengthof the conduit. That is, these properties do not substantially vary atthe macro level, as they do in the embodiments described herein.

Certain embodiments include the realization that the stiffness of thefirst region 213 can be defined in terms of a “drain-back length.” Asshown in FIG. 3, when the tube 201 is engaged with a humidifier 107 orother source of humidified gas, the tube 201 is generally upright at thepoint of engagement. In other words, the slope of a hypothetical linedrawn through the center of the tube 201 is nearly infinite. Withoutsome kind of support holding the tube 201 in this position, theflexibility of the tube 201 naturally causes it to bend at a distanceaway from the point of engagement. Thus, the slope of the hypotheticalline through the center of the tube 201 gradually decreases as thedistance from the point of engagement increases. At a certain distanceaway from the point of engagement, the slope of the hypothetical linereaches zero. After this distance, the slope of the hypothetical linegradually becomes more negative. When the slope of the hypothetical lineis positive, condensate collecting on the tube's wall 211 surroundingthe lumen 209 can theoretically “drain back” into the humidifier 107under the force of gravity. Conversely, when the slope of thehypothetical line is negative, the condensate will theoretically drainaway from the humidifier 107.

Thus, for an unsupported tube 201, the drain-back length 301 can bedefined in terms of the distance between the point of connection to ahumidifier 107 (or other source of humidity) and the point when theslope of the hypothetical line through the center of the tube 201 iszero. In general, the drain-back length 301 is the length of tube 201measured from the point of connection to a humidifier 107 in whichcondensate collecting on the wall 211 surrounding the lumen 209 willnaturally drain back into the humidifier 107. As the first region 213becomes stiffer, the drain-back length 301 increases. If the firstregion 213 is less stiff, the drain-back length 301 decreases. Incertain embodiments, the drain-back length 301 is 350-400 mm (or about350-400 mm), e.g., 380 mm (or about 380 mm). A study was conducted toassess the effect of stiffness on the ability of the tube 201 to allowcondensation on the tube wall 211 to drain back into the humidifier 107.A tube 201 with a thick cladding was connected to an AIRVO humidifiermanufactured by Fisher & Paykel Healthcare Limited in Auckland, NewZealand. The drain-back length was measured to be 380 mm. In order toeliminate the insulating effect of the cladding and focus on the effectof drain-back length, a tube with no cladding was used. The drain-backlength of 380 mm was replicated using a retort stand to hold the tube inplace. The AIRVO humidifier was then turned on and run at a flow rate of15 L/min. A small desk fan was placed 40 cm away from the humidifieroutlet and turned on to the highest setting. This unrealistic draftcondition was imposed to amplify possible condensation. Distal to theretort stand, the tube was allowed to assume a horizontal position lyingon a desk. The AIRVO humidifier and fan were left running for 16 hours.After this time, the tube was removed from the AIRVO humidifier, and thetube was weighed.

By forming a tube 201 such that a significant length is oriented upward(or at least positively sloped) adjacent to the humidified gasesdelivery device, condensation forming in this portion of the tube 201runs back into the humidified gases delivery device. Certain embodimentsinclude the realization that forming the tube 201 with a suitabledrain-back length 301 provides for this upward extension while obviatingthe need for a bulky or complex rigid connector. Referring again to FIG.2A, several properties can affect the stiffness of the conduit 203. Forexample, in at least one embodiment, the fact that the conduit 203 isstiffer adjacent the first opening 205 than it is adjacent the secondopening 207 results from the wall 211 of the conduit 203 being thickeradjacent the first opening 205 than it is adjacent the second opening207. Preferably, the first region 213 has an average wall 211 thicknessof 0.5-2.0 mm (or about 0.5-2.0 mm), or 1.0-2.0 mm (or about 1.0-2.0mm), or 1.1-1.6 mm (or about 1.1-1.6 mm), or 1.6 mm (or about 1.6 mm),or 1.58 mm (or about 1.58 mm), or 1.18 mm (or about 1.18 mm).Preferably, the second region 215 has an average wall 211 thickness of0.1-1.0 mm (or about 0.1-1.0 mm), or 0.1-0.7 mm (or about 0.1-0.7 mm),or 0.1-0.5 mm (or about 0.1-0.5 mm), or 0.2-0.7 mm (or about 0.2-0.7mm), or 0.3-0.6 mm (or about 0.3-0.6 mm), or 0.30 mm (or about 0.30 mm),0.33 mm (or about 0.33 mm), 0.37 mm (or about 0.37 mm), 0.50 mm (orabout 0.50 mm), 0.53 mm (or about 0.53 mm), 0.54 mm (or about 0.54 mm),or 0.56 mm (or about 0.56 mm). A third region 211 intermediate the firstregion 213 and second region 215 can have an average wall 211 thicknessof 0.5-1.0 mm (or about 0.5-1.0 mm), preferably 0.6 mm or thereabout. Incertain embodiments, the average wall 211 thickness is at least 25% (orabout 25%) greater, at least 100% (or about 100%) greater, or at least200% (or about 200%) greater in the first region 213 than in the secondregion 215.

Another example measure of thickness is average thickness per unitlength. Preferably, per unit length, the ratio of average wall 211thickness in the first region 213 to the average wall 211 thickness inthe second region 221 is 1.5:1-5.5:1 (or about 1.5:1-5.5:1), or4.5:1-5.0:1 (or about 4.5:1-5.0:1), or 2.0:2.5 (or about 2.0:2.5). Foran example corrugated tube 201, the ratio can be 4.8:1 (or about 4.8:1),measured at the crests, and 2.2:1 (or about 2.2:1), measured at thetroughs.

In at least one embodiment, the fact that the conduit 203 is stifferadjacent the first opening 205 than it is adjacent the second opening207 results from the wall 211 of the conduit 203 having greater massadjacent the first opening 207 than adjacent the second opening 207. Perunit length, the ratio of average wall 211 mass in the first region 213to the average wall 211 mass of the tube 201 in the second region 215can be 1.5:1-1.9:1 (or about 1.5:1-1.9:1), or 1.5:1-2:1 (or about1.5:1-2:1). The first region 213 can have an average wall 211 mass of50-110 g/m (or about 50-110 g/m), or 65-100 g/m (or about 65-100 g/m),or 65-80 g/m (or about 65-80 g/m), or 70 g/m (or about 70 g/m), or 75g/m (or about 75 g/m). The second region 215 can have an average wall211 mass of 20-50 g/m (or about 20-50 g/m), or 30-50 g/m (or about 30-50g/m), or 30-45 g/m (or about 30-45 g/m), or 35-45 g/m (or about 35-45g/m), or 40 g/m (or about 40 g/m), or 42 g/m (or about 42 g/m). A thirdregion 221 intermediate the first region 213 and second region 215 canhave an average wall 211 mass of 45-65 g/m (or about 45-65 g/m),preferably 50 g/m or thereabout. In certain embodiments, the averagewall 211 mass is at least 25% (or about 25%) greater, at least 100% (orabout 100%) greater, or at least 200% (or about 200%) greater in thefirst region 213 than in the second region 215.

In at least one embodiment, the fact that the conduit 203 is stifferadjacent the first opening 205 than it is adjacent the second opening207 results from the wall 211 of the conduit 203 having greater volumeadjacent the first opening 207 than adjacent the second opening 207. Perunit length, the ratio of average wall 211 volume in the first region213 to the average wall 211 volume in the second region 215 can be1.5:1-3.5:1 (or about 1.5:1-3.5:1), or 2.0:1-3.0:1 (or about2:0:1-3.0:1), or 2.5:1-2.6:1 (or about 2.5:1-2.6:1). The first region213 can have an average wall 211 volume of 1.0-2.0 cm3/cm (or about1.0-2.0 cm3/cm), or 1.0-1.5 cm3/cm (or about 1.0-1.5 cm3/cm), or 1.20cm3/cm (or about 1.20 cm3/cm), or 1.17 cm3/cm (or about cm3/cm). Thesecond region 215 can have an average wall 211 volume of 0.2-1.0 cm3/cm(or about 0.2-1.0 cm3/cm), or 0.40-0.55 cm3/cm (or about 0.40-0.55cm3/cm), or 0.45 cm3/cm (or about 0.45 cm3/cm), or 0.50 cm3/cm (or about0.50 cm3/cm). In certain embodiments, the average wall 211 volume is atleast 25% (or about 25%) greater, at least 100% (or about 100%) greater,or at least 200% (or about 200%) greater in the first region 213 than inthe second region 215.

In at least one embodiment, the fact that the conduit 203 is stifferadjacent the first opening 205 than it is adjacent the second opening207 results from the wall 211 having a greater flex modulus adjacent thefirst opening 205 than adjacent the second opening 207.

FIG. 4A-4E illustrates test equipment for measuring the flex modulus oftubes. The illustrated equipment comprises a commercially-availableInstron machine.

As shown in FIG. 4A, for testing a tube 201, a plug 401 is inserted intoan opening of the tube 201 sample.

As shown in FIG. 4B, the plug 401 is connected to an arm 403 of testwheel 405. The tube 201 is wrapped around the test wheel 405 (which hasa diameter of 78 mm) and is secured by a support wheel 407 which has adiameter of 75 mm. The support wheel 407 touches the tube 201 in orderto secure its position. It does not crush the tube 201 sample. Thelocation of support wheel 407 is adjusted accordingly by adjusting theposition of screws 409 along slots 411 in the supporting frame 413 forthe support wheel 407.

As shown in FIG. 4C, a cord 415 attached to the test wheel 405. Startingfrom a point where the arm 403 of the test wheel 405 is adjacent thesupport wheel 407 and the tube 201 is in an unflexed condition, the cord415 is then pulled at a constant rate of 250 mm per minute for adistance of 100 mm. The tensile load on the cord 415 is recorded as afunction of distance.

The test is repeated with the tube 201 rotated to each of fourorientations about the tube axis (shown in FIGS. 4D and 4E) to accountfor asymmetries in the form of the tube 201. Testing according to thisprocedure provides flexure property data for the tube 201. Testing atube 201 with potentially different flex moduli at locations along thetube 201 comprises testing each region of the tube 201 by cutting outthe region, mounting the region, and testing according to thisprocedure.

For a tested section, the flex modulus is calculated as the gradient ofthe linear portion of the load versus extension plot created through thetest. The flex modulus for the test section is the average flex moduluscalculated for each of the four orientations. By way of example, FIG. 5Aillustrates flexure test data for the four orientations of a section ofcorrugated tube having a tube weight of 100 g/m; FIG. 5B illustratesflexure test data for the four orientations of a section of corrugatedtube having a tube weight of 40 g/m.

FIG. 5C illustrates only the linear portion of the plots of FIG. 5A,with lines of best fit for each orientation of the tube. The line ofbest fit for the tube in a first orientation and has a gradient of0.3377 N/mm. The line of best fit for the tube for a second orientationhas a gradient of 0.3652 N/mm. The line of best fit for the tube in thethird orientation has a gradient of 0.342 N/mm. The line of best fit forthe tube oriented in the fourth position and has a gradient of 0.3506N/mm. The average gradient, and therefore the flex modulus according tothis test calculated for this tube portion is 0.3488 N/mm.

FIG. 5D illustrates an enlarged part of the curves in FIG. 5B, withlines of best fit for each orientation of the tube. The line of best fitfor the tube in a first orientation has a gradient of 0.0208 N/mm. Theline of best fit for the tube in a second orientation has a gradient of0.0194 N/mm. The line of best fit for the tube in a third orientationhas a gradient of 0.0076 N/mm. The line of best fit for the tubeoriented in a fourth orientation has a gradient of 0.0103 N/mm. Theaverage gradient, and therefore the flex modulus measured according tothis test calculated for this tube portion is 0.01452 N/mm.

From these tests, it can be seen that the portion of corrugated tubehaving a tube weight of 40 g/m has a test flex modulus of about 0.015N/mm, while the portion of corrugated tube having a tube weight of 100g/m has a test flex modulus of 0.349 N/mm. Thus, the flex modulus of the100 g/m sample is more than 20 times the flex modulus of the 40 g/mtube.

Per unit length, the ratio of flex modulus in the first region to thatin the second region, as defined by the foregoing test method, can be10:1-250:1 (or about 10:1-250:1), 100:1-220:1 (or about 100:1-220:1), or170:1-200:1 (or about 170:1-200:1), or 188:1 (or about 188:1), or 185:1(or about 185:1). In certain embodiments, the average flex modulus is atleast 25% (or about 25% greater), at least 100% greater, or at least200% greater in the first region than in the second region.

Wall Composition

In at least one embodiment, the wall is formed from an extrudatecomprising one or more polymers. Preferred polymers include Linear LowDensity Polyethylene (LLDPE), Low Density Polyethylene (LDPE),Polypropylene (PP), Polyolefin Plastomer (POP), Ethylene Vinyl Acetate(EVA), Plasticized Polyvinylchloride (PVC), or a blend of two or more ofthese materials. The polymer(s) forms at least 98.4 (or about 98.4),98.5 (or about 98.5), 98.6 (or about 98.6), 98.7 (or about 98.7), 98.8(or about 98.8), 98.9 (or about 98.9), 99.0 (or about 99.0), 99.1 (orabout 99.1), 99.2 (or about 99.2), 99.3 (or about 99.), 99.4 (or about99.4), 99.5 (or about 99.5), 99.6 (or about 99.6), 99.7 (or about 99.7),99.8 (or about 99.8), or 99.9 (or about 99.9) weight percent (wt. %) ofthe total extrudate. In particular embodiments, the extrudate comprises99.488 (or about 99.488) wt. % or about 99.49 (or about 99.49) wt. %LLDPE.

The extrudate can also optionally comprise one or more surface-modifyingagents. A surface-modifying agent is an additive that, either alone orin combination with another substance, affects the properties of amaterial's surface. Such an agent can assist in increasing the surfaceenergy (or the wettability) of the wall surface. Increasing the surfaceenergy can advantageously promote reduced contact angles between dropsor beads of condensate or liquid that may build up on the surface.Specifically, a drop or bead may be spread across a larger surface areaof the wall and, therefore, be more likely to re-evaporate into the gasstream flowing through the lumen.

Including a surface-modifying agent can be particularly advantageous incorrugated tubes. In a corrugated tube, a droplet or bead of condensateis more likely to form in a part of the corrugation of low temperatureposition. The low temperature position is typically a part of thecorrugation closest to or most exposed to ambient conditions surroundingthe tube. Altering the surface properties of the tube wall can allow adroplet or bead formed at the low temperature position to spread acrossthe tube surface and, in doing so, move toward a region of warmertemperature. Such migration of movement of the droplet or bead can allowfor improved re-evaporation rates, both due to the droplet moving towardregions of warmer temperatures, as well as toward regions of the tubewhich are exposed to greater or faster gas stream flows.

Suitable surface modifying agents include glycerol monostearate (GMS),ethoxylated amine, alkanesulphonate sodium salt, and lauricdiethanolamide and additives comprising these substances. MLDNA-418supplied by Clariant (New Zealand) Ltd. and under the product name “418LD Masterbatch Antistatic” is a surface modification agent master batchwith 5(±0.25) % glycerol monostearate (CAS No. 123-94-4) as an activeingredient. Preferably the surface modifying agent comprises at leastabout 0.05 (or about 0.05), 0.1 (or about 0.1), 0.15 (or about 0.15),0.2 (or about 0.2), 0.25 (or about 0.25), 0.3 (or about 0.3), 0.35 (orabout 0.35), 0.4 (or about 0.4), 0.45 (or about 0.45), 0.5 (or about0.5), 1.1 (or about 1.1), 1.2 (or about 1.2), 1.3 (or about 1.3), 1.4(or about 1.4), or 1.5 (or about 1.5) wt. % of the total extrudate. Forexample, in at least one embodiment, the extrudate comprises 0.25 wt. %(or about 0.25 wt. %) of surface modifying agent. As another example, inat least one embodiment, the extrudate comprises 0.5 wt. % (or about 0.5wt. %) of surface modifying agent.

Other methods can also be used to increase surface energy and reducecontact angle. Suitable methods include physical, chemical, andradiation methods. Physical methods include, for example, physicaladsorption and Langmuir-Blodgett films. Chemical methods includeoxidation by strong acids, ozone treatment, chemisorption, and flametreatment. Radiation methods include plasma (glow discharge), coronadischarge, photo-activation (UV), laser, ion beam, electron beam, andgamma irradiation.

By selecting a suitable surface modification method or agent, it ispossible to provide a conduit wall having surface property contactangles of less than 50 (or about 50), 45 (or about 45), 40 (or about40), 35 (or about 35), 30 (or about 30), 25 (or about 25), 20 (or about20) degrees (°), as measurable by an angle measurement device such as ageniometer. For instance, tube walls having surface property contactangles of less than 35° (or about 35°) provide useful results.

TABLE 1 below shows contact angle measurements for various LLDPEsamples, including a sample treated with a surface-modifying agent and asample treated with radiation. The contact angle measurements were basedon static drop shape testing methods conducted in accordance with ASTMStandard D7334, 2008, “Standard Practice for Surface Wettability ofCoatings, Substrates and Pigments by Advancing Contact AngleMeasurement.”

TABLE 1 Average Contact Description of Surface Liquid Angle (degrees)Linear Low-density Polyethylene (LLDPE), Water 97.39 as manufacturedLinear Low-density Polyethylene (LLDPE), Water 67.56 fluorinated, washedLinear Low-density Polyethylene (LLDPE), Water 44.98 plasma-treated, 10%O2, 300 Watts, 30 seconds Linear Low-density Polyethylene Water 33.09(LLDPE), with 5% MLDNA-418 as surface modification agent additive

The sample with 5% MLDNA-418 surface modifying agent produced the lowestmeasured contact angle compared to other surface modification methodstested.

Foam

The tube wall described above can be formed from polymer foam in certainembodiments. Foam is a solid material having gas voids dispersedthroughout. The voids can be open cell or reticulated (such that amajority, e.g., 51-100%, of the voids interconnect with other voids).The voids can also be closed cell so that most (e.g., 80%, 90%, or more)of the cells do not interconnect with other voids. Foams with open-cellvoids can be advantageous because they are generally less dense, requireless material, and consequently are less expensive to produce than foamwith closed-cell voids. Preferably, however, the voids are closed cell,which improves and better controls the insulating properties of thewall. Foams with closed-cell voids can have the additional advantage ofbeing easier to manufacture than foams with open-cell voids.

In embodiments comprising a foam wall, the foam wall is preferably asingle piece of polymer foam, for example being formed by extrusion of asingle extrudate.

A foam wall can advantageously provide an improved level of thermalinsulation for the lumen, compared with the level of thermal insulationprovided by a non-foam wall. Thus, in at least one embodiment, the wallis thermally insulative of the contents (such as for example humidifiedgases flowing through the gas flow passage) of the elongate conduit tothe potential cooling effects of the environment surrounding the medicaltube (for example, insulating from the ambient air surrounding abreathing circuit, or a laparoscopic insufflation system). Theenvironment surrounding the medical tube is for example, a hospital wardor room, an operating theater, a home bedroom, or other locations wherethe patient may be located.

In various embodiments, a foam wall has or provides for a thermalconductivity of 0.2-0.4 W/m-K (Watts per meter Kelvin) (or about 0.2-0.4W/m-K). It will be appreciated, however, that a foam wall canbeneficially provide for other levels of thermal conductivity, andthermal conductivities of 0.15-0.35 W/m-K (or about 0.15-0.35 W/m-K) or0.25-0.45 W/m-K (W/m-K) are also contemplated.

An example method for forming a foam wall includes the addition of achemical foaming agent to the extrudate. Chemical foaming agents aresometimes also referred to as blowing agents. A chemical foaming agentenables foaming of the extrudate material as part of or after theextrusion process, which is explained in greater detail below. Thechemical foaming agent can comprise at least 0.005 (or about 0.005),0.006 (or about 0.006), 0.007 (or about 0.007), 0.008 (or about 0.008),0.009 (or about 0.009), 0.01 (or about 0.10), 0.011 (or about 0.011),0.012 (or about 0.012), 0.013 (or about 0.013), 0.014 (or about 0.014),0.015 (or about 0.015), 0.016 (or about 0.016), 0.017 (or about 0.017),0.018 (or about 0.018), 0.019 (or about 0.019), or 0.02 (or about 0.02)wt. % of the total extrudate. For example, the chemical foaming agentcan comprise 0.01-0.012 (or about 0.01-0.012) wt. % of the totalextrudate. As part of a chemical foaming extrusion process, the polymercomponent of an extrudate is mixed with a chemical foaming agent. Somepreferred chemical foaming agents comprise calcium oxide. For example,MHYNA-CF20E supplied by Clariant (New Zealand) Ltd. under the productname Hydrocerol CF20E is a chemical foaming agent in the form of ablowing agent master batch with about 0.5-1% calcium oxide as an activeingredient.

During a chemical foam extrusion process the polymer resin component andchemical foaming agent(s) are mixed and melted. The chemical foamingagent(s) decomposes and liberates gas which is dispersed in the polymer(or master batch or extrudate) melt and which expands upon exiting thedie of an extruder.

It will also be appreciated other foaming techniques can be employed forforming a foam wall, such as by physical rather than chemical foamingmethods. Physical foaming methods include gas being introduced directlyinto the extrudate while under pressure. As the extrudate is extruded,the pressure is reduced allowing the gas to expand. For example, onesuch physical foaming technique includes blowing or injecting of gas(es)into the extrudate at or near the point of extrusion. Such gas(es) mayinclude nitrogen, carbon dioxide, pentane or butane.

Sheath

In certain embodiments, the elongate conduit 203 can further comprise asheath 227, as shown in FIG. 2C. A sheath 227 is a member partially orfully surrounding the wall 211. The sheath 225 can be secured to thewall 211 of the conduit 203 at locations along the wall 211 or may besecured only to ends of the tube 201. The sheath 227 can be used tosecure conductive filaments (described below) in place and/or to preventheat loss due to cool air currents impinging on the tube wall 211.

Although the sheath 227 can be incorporated into a conduit 203comprising a smooth wall (not shown) or a corrugated wall 211, it can beparticularly advantageous to include such a sheath 227 with a corrugatedwall. The sheath can trap air between adjacent outer crests (or annularprotrusions) of the corrugations. This may assist in further insulationof the gas passing through the lumen 209.

For delivery tubes incorporating a sheath 227, the sheath 227 may beapplied about wall 211 as an extruded outer layer, as a wrapping aboutthe wall 211, or as a sleeve that is slid or pulled into position aboutthe wall 211. Such a sheath 227 may be formed of similar materials asthe wall 211 (described above), for example LLDPE. The sheath 227 mayassist in further improving thermal performance of tube 201.

The sheath 227 may be of any necessary thickness, although thickness andthe material used should be balanced with the need to maintainflexibility of the conduit 203. In one embodiment, it is contemplatedthe sheath 227 may have an average wall thickness of 100 microns (orabout 100 microns).

However, the average thickness per unit length, average mass per unitlength, average volume per unit length, or flex modulus can vary at themacro level along the length of the sheath 227. In some embodiments, theproperty measure can be greater at one region of the sheath 227 adjacentone end of the tube 201 than a region of the sheath 227 adjacent theother end. In other embodiments, the property measure may vary graduallyalong the length of the sheath 227. In other embodiments, the propertymeasure may have distinct transitions moving along the length of thesheath 227. In some embodiments, the measure or characteristic may begreater at a region adjacent one end of the tube 201 than in a region atthe mid-length portion of the tube 201 and may be greater at a regionadjacent the other end of the tube 201 than at a region at themid-portion of the tube 201.

For instance, the external sheath 227 can be thicker at the humidifierend of the tube 201 to better insulate the tube 201 and prevent heatloss where most of the condensation is likely to occur. A thicker sheath227 at the humidifier end can also add to the stiffness of the tube 201so it maintains a more vertical position for a greater distance, beforebending toward the horizontal, thereby increasing drain-back length (notshown). In this way, more condensation is returned to the humidifier(not shown), rather than entering the breathing tube 201. A thinnersheath 227 at the patient end can increase flexibility and reduce weightto improve the comfort of the user.

Where a sheath 227 is extruded about the wall 211, for example, such anextrusion could be a sequential step to initial extrusion of the wall211, that is, an extrusion step post-formation of the wall 211. Further,where an outer sheath 227, for example, is a wrap about the wall 211,the sheath 227 may be constructed in place from a tape or ribbonspirally wound about the length of the wall 211. Still further, where anouter sheath 227 is pre-formed as a hollow tube, it may be sleeved intoposition about the outside of the wall 211.

Conductive Filaments

In certain embodiments, a tube 201 can further comprise one or moreconductive filaments. These conductive filaments may be heatingfilaments and/or sensing filaments.

A filament can, for example, take the form of a wire or tape on or inthe wall of the conduit. FIG. 6 illustrates an example placement of aheater wire 601 within the lumen 209 of a tube 201. Although thefilament can be within the lumen 209, it can be desirable to move thefilament out of the gas flow path. For example, the filament can beplaced on the wall radially opposite the lumen or inside the wall. FIG.7 illustrates the placement of a heater wire 601 about the externalsurface of the wall 211. Such placement can reduce the risk of ignitionin an oxygen-rich gas flow and also improve laminar gas flow.

Materials for such filaments are conductive metals including copper oraluminum, or a PTC (positive temperature coefficient) type material.Aluminum is not as conductive as copper, but may be an economical choiceeven though the wire diameter is larger for the same resistance. Whilethe applied circuit voltage is intrinsically safe (less than 50V), forcorrosion resistance and electrical safety in the event of the wall orsheath being damaged, the wire will ideally be self-insulated, either byenamel coating, or anodizing in the case of aluminum.

In certain embodiments, a filament can be placed on the outer surface ofthe wall 211 (radially outward from the lumen 209), and a plastic sheath227 can be fitted about the filament. In such a configuration, thesheath 227 can help to restrain the filament in position. Moreover, thesheath can also be included when the filament is placed in the lumen 209or in the wall 211. As explained above, an insulating external sheath227 prevents heat loss. However, the outer sheath 227 may be employed,regardless of whether a filament is also included.

Comparison with Uniform-Stiffness Tubes

FIG. 8 compares the condensate accumulation in uniform-stiffness tubesto that in a variable-stiffness tube. In this experiment, threeuniform-stiffness tubes and one variable-stiffness tube were connectedin circuit with sources of humidified gas and placed in a test chamberwith a cooling flow of air simulating a typical hospital ward withconditioned air flowing over the circuit. The condensate thataccumulated over a 16-hour period was collected and weighed. The resultsindicated the increasing the mass of the wall in the uniform-thicknesstubes from 50 g/m to 63 g/m to 74 g/m reduced condensate accumulation.The variable-stiffness tube, made from three sections having a mass of74 g/m at the first end, 63 g/m in an intermediate region, and 50 g/m atthe second end, unexpectedly accumulated even less condensate than the74 g/m tube.

One explanation for the unexpectedly improved performance of thevariable-stiffness tube over the stiffest uniform-thickness tube may bethe interaction with the humidifier that served as the source ofhumidified gas. The MR850 Humidifier, manufactured by Fisher & PaykelHealthcare Limited of Auckland, New Zealand, detects the patient-endtemperature and controls the heater plate under the chamber and heatingfilament in the tube. The algorithm used by the humidifier involvesputting gas into a tube, fully saturated, at 37° C., then heating thetube so that the temperature sensed at the end of the tube measures 40°C. Because the 50/63/74 g/m variable-stiffness tube has a relativelythin wall at the patient end, the temperature is lower at the patientend than it is at the patient end of the 74 g/m uniform-wall tube. Thus,the humidifier's control algorithm puts more power into the heater plateand heating filament with the variable-stiffness sample, resulting inless condensation at the humidifier-end of the tube.

Component in Medical Circuits

Reference is next made to FIG. 9, which shows an example medical circuitaccording to at least one embodiment. The circuit comprises avariable-stiffness tube as described above for the inspiratory tube 103.The properties of the inspiratory tube 103 are similar to the tubesdescribed above. The inspiratory tube 103 has an inlet 109,communicating with a source of humidified gas 115, and an outlet 113,through which humidified gases are provided to the patient 101. Asdescribed above, heater wires 601 can be placed within the inspiratorytube 103 to reduce the risk of rain out in the tubes by maintaining thetube wall temperature above the dew point temperature.

In FIG. 9, an expiratory tube 117 is also provided. The expiratory tube117 also has an inlet 109, which receives exhaled humidified gases fromthe patient, and an outlet 113. As described above with respect to FIG.1, the outlet 113 of the expiratory tube 117 can vent exhaled gases tothe atmosphere, to the ventilator/blower unit 115, to an airscrubber/filter (not shown), or to any other suitable location.

The expiratory tube is optional, however. Inspiratory tubes 103according to the above-described embodiments can be used with otherforms of respiratory support, for example using a standalone blowerhumidifier without an expiratory return path. Examples of such productsinclude the humidified CPAP delivery products and COPD therapy productsof Fisher & Paykel Healthcare Limited of Auckland, New Zealand. In thesesystems, a combined blower/humidifier supplies humidified gases to theconnected delivery tube. The delivery tube supplies these gases to apatient interface connected to the patient end of the delivery tube. Thepatient interface is typically a full face mask, nasal mask, nasalpillows for CPAP therapy, nasal prongs or nasal cannula for COPD therapyor a tracheal connector of an intubated patient where the device may beused to assist a transition off full ventilation.

Component of an Insufflation System

Laparoscopic surgery, also called minimally invasive surgery (MIS), orkeyhole surgery, is a modern surgical technique in which operations inthe abdomen are performed through small incisions (usually 0.5 to 1.5cm) as compared to larger incisions needed in traditional surgicalprocedures. Laparoscopic surgery includes operations within theabdominal or pelvic cavities. During laparoscopic surgery withinsufflation, it may be desirable for the insufflation gas (commonlyCO2) to be humidified before being passed into the abdominal cavity.This can help prevent “drying out” of the patient's internal organs, andcan decrease the amount of time needed for recovery from surgery.Insufflation systems generally comprise humidifier chambers that hold aquantity of water within them. The humidifier generally includes aheater plate that heats the water to create a water vapour that istransmitted into the incoming gases to humidify the gases. The gases aretransported out of the humidifier with the water vapor.

Reference is next made to FIG. 10, which shows an insufflation system1001, according to at least one embodiment. The insufflation system 1001includes an insufflator 1003 that produces a stream of insufflationgases at a pressure above atmospheric for delivery into the patient 1005abdominal or peritoneal cavity. The gases pass into a humidifier 1007,including a heater base 1009 and humidifier chamber 1011, with thechamber 1011 in use in contact with the heater base 1009 so that theheater base 1009 provides heat to the chamber 1011. In the humidifier1007, the insufflation gases are passed through the chamber 1011 so thatthey become humidified to an appropriate level of moisture.

The system 1001 includes a delivery conduit 1013 that connects betweenthe humidifier chamber 1011 and the patient 1005 peritoneal cavity orsurgical site. The conduit 1013 is a variable-stiffness tube asdescribed above. The conduit 1013 has a first end and second end, thefirst end being connected to the outlet of the humidifier chamber 1011and receiving humidified gases from the chamber 1011. The second end ofthe conduit 1013 is placed in the patient 1005 surgical site orperitoneal cavity and humidified insufflation gases travel from thechamber 1011, through the conduit 1013 and into the surgical site toinsufflate and expand the surgical site or peritoneal cavity. The systemalso includes a controller (not shown) that regulates the amount ofhumidity supplied to the gases by controlling the power supplied to theheater base 1009. The controller can also be used to monitor water inthe humidifier chamber 1011. A smoke evacuation system 1015 is shownleading out of the body cavity of the patient 1005.

The smoke evacuation system 1015 can be used in conjunction with theinsufflation system 1001 described above or may be used with othersuitable insufflation systems. The smoke evacuation system 1015comprises a discharge or exhaust limb 1017, a discharge assembly 1019,and a filter 1021. The discharge limb 1017 connects between the filter1021 and the discharge assembly 1019, which in use is located in oradjacent to the patient 1005 surgical site or peritoneal cavity. Thedischarge limb 1017 is a self-supporting tube (that is, the tube iscapable of supporting its own weight without collapsing) with two openends: an operative site end and an outlet end.

At least one embodiment includes the realization that the use of avariable-stiffness tube as the conduit 1013 can deliver humidified gasesto the patient 1005 surgical site with minimized heat loss. This canadvantageously reduce overall energy consumption in the insufflationsystem, because less heat input is needed to compensate for heat loss.

Methods of Manufacture

The conduit, sheath or both of the delivery tube may be manufacturedaccording to a number of processes, adapted to provide for stiffnessvariation in the tube. The conduit and sheath may be formed by the samemanufacturing method, or by different manufacturing methods. In somemanufacturing methods, the tube and sheath may be integrated during themanufacturing method such that the sheath is connected to the conduit atnumerous locations along the length of the tube or along one continuousspiral along the length of the tube. Alternatively, the sheath mayfreely surround the conduit and only connect with the conduit at oradjacent the end connectors.

Typically the conduit, the sheath, or both may be made from one or moreextruded polymer components. The properties of the extrudate (includingcomposition, surface-modifying agents, methods for increasing surfaceenergy, and foaming agents) is described above.

A first manufacturing method is described with reference to FIG. 11. Themethod comprises extruding an elongate conduit having a longitudinalaxis, a lumen extending along the longitudinal axis, and a wallsurrounding the lumen, wherein the wall is stiffer in a first length ofthe conduit than in a second length of the conduit. The method can alsoinvolve corrugating the elongate conduit, such as with a corrugatingdie. More specifically, the process involves mixing or providing of amaster batch of extrudate material (i.e. material for extrusion),feeding the master batch to an extrusion die head, extruding theextrudate as described above, and (optionally) feeding the elongateconduit into a corrugator using an endless chain of mold blocks to forma corrugated tube.

FIG. 11 generally illustrates a setup where there is provided a feedhopper 1101 for receiving raw ingredients or material (e.g. master batchand other materials) to be passed through a screw feeder 1103 driven bya motor 1105 in direction A toward a die head 1107. The molten tube 1109is extruded out of the die head 1111. Conductive filaments canoptionally be co-extruded on or in the molten tube 1109. The method canfurther comprise one or more spiral-extrusion processes thatprogressively add layers of material in order to create portions ofdifferent stiffness along the tube. Such spiral-extrusion processes aredescribed in greater detail below.

An extruder such as a Welex extruder equipped with a 30-40 mm diameterscrew and, typically, a 12-16 mm annular die head with gap of 0.5-1.0 mmhas been found to be suitable for producing low cost tubes quickly.Similar extrusion machines are provided by American Kuhne (Germany),AXON AB Plastics Machinery (Sweden), AMUT (Italy), and Battenfeld(Germany and China). A corrugator such as those manufactured andsupplied by Unicor® (Hassfurt, Germany) has been found to be suitablefor the corrugation step. Similar machines are provided by OLMAS (CarateBrianza, Italy), Qingdao HUASU Machinery Fabricate Co., Ltd (QingdaoJiaozhou City, P.R. China), or Top Industry (Chengdu) Co., Ltd.(Chengdu, P.R. of China).

During manufacture, the molten tube 1109 is passed between a series ofrotating molds/blocks on the corrugator after exiting the extruder diehead 1111 and is formed into a corrugated tube. The molten tube isformed by vacuum applied to the outside of the tube via slots andchannels through the blocks and/or pressure applied internally to thetube via an air channel through the center of the extruder die core pin.If internal pressure is applied, a specially shaped long internal rodextending from the die core pin and fitting closely with the inside ofthe corrugations may be required to prevent air pressure escapingendways along the tube. The corrugator speed can be varied to achievedifferent wall thickness. Slower corrugator speed gives a thicker wall,and faster speed gives a thinner wall.

The tube may also include a plain cuff region for connection to an endconnector fitting. Thus, during manufacture, a molded-plastic endconnector fitting can be permanently fixed and/or air tight by frictionfit, adhesive bonding, over moulding, or by thermal or ultrasonicwelding.

Another suitable method for manufacturing a tube according to theembodiments described here involves spiral forming, as shown in FIG. 12.In general, the method comprises extruding a tape, wherein a firstlength of the tape is stiffer that a second length of the tape; spirallywinding the extruded tape around a mandrel such that adjacent turns ofthe extruded tape touch or overlap, thereby forming an elongate conduithaving a longitudinal axis, a lumen extending along the longitudinalaxis, and a wall surrounding the lumen, wherein the wall is stiffer in afirst length of the conduit than in a second length of the conduit. Themethod can also include optionally corrugating the elongate conduit.

The extrusion process involves mixing or providing of a master batch ofextrudate material (i.e. material for extrusion), feeding the masterbatch to an extrusion die head, extruding the extrudate into a tape.

Then, the extruded or pre-formed tape is wound helically so that withineach turn, one edge of the tape overlaps an edge of a preceding turn andunderlaps an edge of a succeeding turn. Such spirally wound conduits canbe made with a single helically disposed tape or multiple helicallydisposed tapes interleaved. In some embodiments, a reinforcing beadoverlays the overlap between turns of tape. The bead may provide ahelical reinforcement against crushing for the tube and may also providea source of heat, chemical or mechanical adhesive for fusing or joiningthe lapped portions of tape. In some examples, a double wall conduit canbe constructed by laying additional tape, or portions of the same tape,over the outside, supported on the helical ridge formed by the bead.

In this method, the stiffness of the tube depends upon the stiffness ofthe tape, and the stiffness of the tube can be adjusted by changing thethickness, mass, volume, flex modulus, etc. of the tape. A tube havingvariable wall thickness along its length may be constructed according tothis process by varying the thickness of the tape so that, for example,in a first region, the tape may have a thickness that is greater than inanother region, where the thickness may be slightly thinner, and thesecond region where the thickness may be thinner still.

Another suitable method for spiral forming comprises extruding a tapehaving a generally uniform stiffness; spirally winding the extruded tapearound a mandrel such that adjacent turns of the extruded tape touch oroverlap, thereby forming an elongate conduit having a longitudinal axis,a lumen extending along the longitudinal axis, and a wall surroundingthe lumen, wherein the wall is stiffer in a first length of the conduitthan in a second length of the conduit. The method can includescorrugating the elongate conduit, to provide a conduit having avariable-stiffness wall. For example, the corrugator speed can be variedto achieve different wall thickness. Slower corrugator speed gives athicker wall, and faster speed gives a thinner wall.

Shown in FIG. 12 is a molten extruded tube 1201 exiting the die 1203 ofan extruder before passing into a corrugator 1205. On exiting thecorrugator 1205, a heater wire 601 is wound about the exterior of theformed tubular component 201.

One advantage of the preferred type of the tube manufacture describedabove with reference to FIG. 12 is that some of the mold blocks B caninclude end cuff features that are formed at the same time as thetubular component 201. Manufacture speeds can be significantly increasedby the reduction in complexity and elimination of secondarymanufacturing processes. While this method is an improvement overseparate cuff forming processes, a disadvantage of the prior art plaincuff is that the corrugator must slow down to allow the wall thicknessof the tube in this area to increase (the extruder continues at the samespeed). The cuff thickness is increased to achieve added hoop strengthand sealing properties with the cuff adaptor fitting. Further, the heatof the molten polymer in this thicker region is difficult to removeduring the limited contact time with the corrugator blocks and this canbecome an important limiting factor on the maximum running speed of thetube production line.

The foregoing description of the invention includes preferred formsthereof. Modifications may be made thereto without departing from thescope of the invention. To those skilled in the art to which theinvention relates, many changes in construction and widely differingembodiments and applications of the invention will suggest themselveswithout departing from the scope of the invention as defined in theappended claims. The disclosures and the descriptions herein are purelyillustrative and are not intended to be in any sense limiting.

The invention claimed is:
 1. A medical tube for providing humidified gasto a patient, comprising: a first connector; a second connector; anelongate conduit extending between the first connector and the secondconnector, the conduit having a first end connected to the firstconnector, a second end connected to the second connector, a firstopening at the first end, the first opening configured in size and shapeto connect to a source of humidified gas such that the first openingreceives humidified gases from the source of humidified gas, a secondopening at the second end, the second opening configured in size andshape to connect to a patient interface such that the second openingexpels humidified gases to the patient through the patient interface, alongitudinal axis, a lumen extending between the first opening and thesecond opening along the longitudinal axis, and an extruded wallextending between the first opening and the second opening andsurrounding the lumen, wherein a first portion of the extruded wallsurrounding the first opening has a first stiffness and a second portionof the extruded wall surrounding the second opening has a secondstiffness, wherein the first stiffness is greater than the secondstiffness, and wherein a third stiffness of a third portion of theextruded wall in a region of the conduit between the first portion andthe second portion of the extruded wall is intermediate the firststiffness and the second stiffness.
 2. The medical tube of claim 1,wherein the extruded wall comprises an extruded material which comprisesone or more surface modification agents.
 3. The medical tube of claim 1,wherein a thickness of the first portion of the extruded wallsurrounding the first opening is between about 0.5 mm and about 2.0 mm,and a thickness of the second portion of the extruded wall surroundingthe second opening is between about 0.1 mm and about 1.0 mm.
 4. Themedical tube of claim 1, wherein a mass of the first portion of theextruded wall surrounding the first opening is between about 50 g/m andabout 110 g/m, and a mass of the second portion of the extruded wallsurrounding the second opening is between about 20 g/m and about 50 g/m.5. The medical tube of claim 1, wherein a volume of the first portion ofthe extruded wall surrounding the first opening is between about 1.0cm³/m and about 2.0 cm³/m, and a volume of the second portion of theextruded wall surrounding the second opening is between about 0.2 cm³/mand about 1.0 cm³/m.
 6. The medical tube of claim 1, wherein the ratioof flex modulus of the first portion of the extruded wall surroundingthe first opening to flex modulus of the second portion of the extrudedwall surrounding the second opening is between about 10:1 and about250:1.
 7. The medical tube of claim 1, wherein the extruded wall is asingle piece of polymer foam formed by extrusion of a single extrudate.8. The medical tube of claim 1, wherein the first portion of theextruded wall surrounding the first opening has a first thickness andthe second portion of the extruded wall surrounding the second openinghas a second thickness, wherein the first thickness is greater than thesecond thickness.
 9. The medical tube of claim 1, wherein the firstportion of the extruded wall surrounding the first opening is configuredto extend vertically upward from the source of humidified gas without asupport holding the first portion when the first opening is connected tothe source of humidified gas, the first portion of the extruded walldefining a drain-back length.
 10. The medical tube of claim 1, whereinthe extruded wall is corrugated.
 11. The medical tube of claim 1,wherein the first portion of the extruded wall surrounding the firstopening is configured to extend vertically upward from the source ofhumidified gas, the first portion of the extruded wall defining adrain-back length.
 12. The medical tube of claim 11, wherein thedrain-back length is between about 350 mm and about 400 mm.
 13. Themedical tube of claim 1, further comprising one or more conductivefilaments in or on the conduit.
 14. The medical tube of claim 13,wherein at least one of the one or more conductive filaments is aheating wire.
 15. The medical tube of claim 13, wherein at least one ofthe one or more conductive filaments is a sensing wire.
 16. The medicaltube of claim 1, wherein the extruded wall comprises an extrudedmaterial, wherein the extruded material is foam.
 17. The medical tube ofclaim 16, wherein the foam is closed-cell foam.
 18. The medical tube ofclaim 1, further comprising a sheath surrounding at least a portion ofan outer surface of the elongate conduit.
 19. The medical tube of claim18, wherein the sheath comprises an extruded material extruded around atleast a portion of the outer surface of the elongate conduit.
 20. Themedical tube of claim 18, wherein the sheath comprises a materialgenerally spirally wrapped around at least a portion of the outersurface of the elongate conduit.
 21. The medical tube of claim 18,wherein the sheath comprises a sleeve material sleeved around at least aportion of the outer surface of the elongate conduit.
 22. The medicaltube of claim 18, wherein the sheath comprises a sheath wall and thesheath wall is stiffer in a first region of the sheath than in a secondregion of the sheath.
 23. The medical tube of claim 22, wherein thesheath wall is stiffer proximate the first opening of the conduit thanthe sheath wall proximate the second opening of the conduit.
 24. Themedical tube of claim 22, wherein the sheath wall is stiffer proximatethe second opening of the conduit than the sheath wall proximate thefirst opening of the conduit.